This application relates to a geared gas turbine engine, wherein a gear reduction is provided with only four star gears.
Gas turbine engines are known and typically include a fan delivering air into a bypass duct as bypass air and into a compressor. The air delivered into the compressor is mixed with fuel and ignited. Products of this combustion pass downstream over turbine rotors driving them to rotate. The turbine rotors, in turn, drive the compressor and fan rotors.
Historically, a fan rotor was driven at the same speed as a fan drive turbine rotor. This somewhat limited the design of the gas turbine engine. It was desirable that the fan rotate at a slower speed and have an increased diameter. However, it was also desirable that the turbine rotate at faster speeds. Thus, compromises had to be made.
More recently, a gear reduction has been incorporated between the fan drive turbine and the fan rotor. This has allowed the size of the fan rotor to increase. At the same time, the turbine rotor can rotate at increased speed.
The gear reductions utilized today have utilized epicyclic planetary or star gear reductions. These gear reductions have always utilized at least five star gears between a sun gear and a ring gear. This has limited the available gear ratios.